In order to improve brake performance (braking performance) on ice, increasing the number of sipes in the tread portion and narrowing the intervals between the sipes has conventionally been carried out. Additionally, giving the sipe depth direction a zigzag shape to further improve on-ice brake performance has also been carried out (e.g., see patent documents 1 to 4).                Patent Document 1: JP-A No. 2003-118332        Patent Document 2: JP-A No. 10-258615        Patent Document 3: JP-A No. 8-99506        Patent Document 4: EP 0864448 B1        